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A Barn Door Tracker mount is an inexpensive and very effective solution for taking long exposures of the night sky without producing star trails.
UPDATED DESIGN: After using the original design with some great results, I recently found some areas where big improvements could be made, including camera placement and laser polar alignment.
Using a pivoting drive bolt increases the mount’s accuracy (and tracking time) by around 3-4 times over a regular fixed-position (tangent) drive bolt. The completed pivoting drive bolt can be mounted by drilling a hole (roughly 20mm in diameter) through the top board. A small washer (or small nut) should then be glued on to the bottom board where the dome nut meets the bottom board. The barn door tracker can also be built using an M6 sized drive bolt instead of the M8 size shown. Many sites recommend using the second hand of an analogue watch to keep time (by mirroring the position of the second hand around the clock face). I realised it’d be easier to take eyesight out of the process by playing a beep at set intervals, indicating when the handle should be at the next point. My first attempt gave some poor results, with the stars forming little circles or semi circles (depending on the exposure length). The camera can be mounted anywhere on the top board, but should have as much room for manoeuvre as possible as it can be tricky to frame subjects. Although not necessary for wide angle shots or shorter exposures, adding a laser or a finder scope to the tracker will increase your polar alignment accuracy over the regular sighting tube (see polar alignment section). Of the two, I prefer the green laser option as it doesn’t involve grovelling on the floor or contorting your body trying to look through the scope. For best visibility the laser should be green as most other colours (especially red) will be too difficult to see.
Warning: Although polar alignment will only take a few seconds with the laser method, it’s worth saying that it may make you a bit conspicuous!
Many modern lenses don’t have distance scale which makes manual focusing tricky, especially in the dark.
If the temperature is much lower outdoors than it is indoors, you should allow 20 minutes or so for your lens to adapt to the new temperature before you focus the lens, as the infinity focus point of lenses changes with temperature. Shooting in RAW maximises the data held in the images, giving much better results with the stacking process.
When you’re out in the dark the images can look overexposed on the camera screen, so I turn the brightness down. The offset of the NCP from Polaris is handily in the direction of the brightest star in Ursa Minor, which can be used as a wide-view guide to make sure you’re aligned in the right direction. Motorized Barn Door TrackerThe Barn Door mount gets it's name from the fact that it's basically a wooden board with a door hinge.
With Instructables you can share what you make with the world, and tap into an ever-growing community of creative experts. Mostly hand tools were used with the exception of a mitre saw to get the ends for the hinge mount nice and square. The motor used is a 230v ac synchronous 1 rpm which is very accurate as it relies on the 50 Hz frequency of the main ac supply.
I've always liked astrophotography, but it always seemed so expensive to get into, beyond short wide angle exposures. Once, I had run across the idea of a barn door tracker, which seemed like a clever but more importantly a cheap solution to longer exposures. I tried and failed to make sense of the cloudbait excel spreadsheet, which he used to calculate his step rates, but decided to try building my own anyways. It's an isosceles-type barn door tracker (pivot on motor and drive nut) with AltAzimuth adjustments, as it was to be mounted on a stand without any adjustments rather than an expensive tripod. Mechanical design is nothing fancy - the tracker is just two hinged boards being pushed apart by a threaded rod, driven by a stepper motor.
The precision of fabricating the tracker is less important than your ability to measure what you've done. If you are going to build axes, you only don't really need all that much travel - they're for fine alignment. The precision required for measurement is directly proportional to what focal lengths you want to use. With this mechanical approach, tweaking of code will be required - this isn't exactly a grab and go solution, and I'm not sure if it was the best route as I'm still having some tracking issues at the longest focal lengths of my lens.
If you're going to directly drive the rod with a stepper, I'd recommend using micro stepping in order to produce smooth movement, and make sure the stepper has relatively small steps to begin with. Here's a diagram of the math involved, and how to get the input values for the calculator program.
Generally, RPM must decrease over time to maintain the same angular velocity (chart), in an isosceles tracker. To figure out the lengths of sides A and B, measure the distance from the board to the pivot point for both top and bottom, then measure the length along the board to the hinge. FormulasThese are the two formulas the calculator uses in figuring out the table of values used. Main code (zip file) of the calculator is pretty simple: the program selects the most accurate delay at t=0, using the derivative above, then every $INTERVAL steps it calculates the error at the current rate, and if it reduced by slowing down or speeding up.
On power on, it will rewind at 7.1x rate until the limit switch is hit, at which point it advances slightly then waits for the user to press the button, at which point it will run forward at the sidereal rate. A diagram of how the stars rotate in the night sky, relative to polaris and the north celestial pole. To actually use the mount, you have to align it so the hinge points to Polaris, The North Star.
For the AVR, I used a Attiny85 as it was what I had handy, but you could get away with a Attiny25 just fine.
The header to the right is the ISP header, to allow me to program the microcontroller without removing it. In the AVR code, I used a clever trick to allow the RESET pin to be used as the user input. My code uses a delayMicroseconds for a 20mhz uC; you will need to use a different one if your crystal value differs. I used a chinese Saleae Logic clone to figure out the number of dead cycles to add to get timing accuracy just right - ended up about 400 microseconds fast over 70 minutes; plenty accurate. Programming the AVR was done via ArduinoISP running on a Teensy 2.0 until I killed it in the same incident that claimed the first stepper board (12v to logic supply), I then programmed it via a ATTiny-based usbtinyisp programmer.
Finderscope bracket: Mounted by drilling a single hole in it and running a screw through it. An earlier version of the altitude adjustment is where I figured out how to make plastic chunks out of milk jugs. Azimuth axis: Two board chunks are mounted with one big bolt with a washer between the boards and a nylock nut. Azimuth axis pivot nut: This was a normal nut that I ground down with a dermal and some cutting disks to have two lugs which fit nice and tight into the holes of mecanno. Mount drive pivot nut: tacked 3 nuts together with solder, then stuck two machine screws on the middle nut with superglue. Servo drive: In a HP printer carcass, a stepper was set up with a worm drive already to raise and lower the print head. An alternative to a finder scope is a reflex sight (no magnification), such as a straw with a crosshair or telrad finder, but be advised that a reflex sight will be just about useless in an area with light pollution, or if you have shitty eyes (like me). Initially I had 2+ turns of dead space in the azimuth axis, but I've found that alignment is crucial at longer focal lengths; sometimes I've had to fine tune alignment by making exposures and tweaking the axes until there is no visible trailing.
You can get useful bits of plastic stock by cutting up a milk jug into strips then melting them together with a heat gun. Before pegging an exposure as poorly focused, try a short exposure with extremely high ISO sensitivity first.
The price for the "polarie" type trackers is criminal; I intend to try to build one sometime as they aren't much more than a camera mount being rotated at a constant rate.
But after looking into the cost of all the components (accurate stepper motor, arduino, motor controller and suitable gears would come to around ?80-100 altogether), along with the complexity of building the circuits, coding the arduino and finding the right gears – you may as well put the money towards a dedicated tracking platform instead! Fortunately any mounts built to the original design can easily be adapted to the new layout.
This makes composing much easier and improves the tracking performance through better balance.

For this a 9mm diameter hole should be drilled into the side of the top board to a depth of at least 5cm. Shown below is the simplified solution I arrived at after struggling with a clumsy pivot assembly design described online.
This allows the drive bolt to remain seated in exactly the same place while the handle is rotated. The best option is to use a piano hinge available here which can cover the full width of the boards, be cut to the correct size and so spread the load evenly. In fact an M6 version has the potential to be more accurate than the M8 version due to the finer thread.
I always felt this was a bad idea as it’s hard to see the watch in the dark, let alone the second hand! I created an audio file to do this which can be played on a loop via a phone or MP3 player to do its job of time keeping. I used a sample sized sheet of glow in the gark vinyl, which glows for several hours after a second or two under torch light. Placing it nearer to the hinge is advisable as this reduces the load on the handle, and prevents the handle from getting in the way of the camera.
It also makes things easier as you can see the entire sky, allowing you to get your bearings and attain a good alignment much quicker. If you don’t have a finder scope bracket for the laser, you can build one by simply drilling a hole lengthways through a column of wood to accommodate the laser with a few mm of room on all sides. The most accurate method I’ve found is to use live view to zoom in and focus on a star of medium brightness.
To prevent this I use PVC insulation tape on the lens to strap the focus ring in place and stop the focus from shifting. These photos go to prove that you don’t need to spend thousands of pounds on a telescope and an expensive mount. With the laser or finder scope this usually takes less then a minute, but you have to know exactly where the North Celestial Pole (NCP) is (and be able to see it – the stars are pretty faint) to get good alignment. While there are many commercial mounts to track the sky, here we will discuss a simple way to construct a mount that will costs less than $100 complete with a motor to drive the screw.The mount must turn at exactly the speed of the rotation of the earth but in the opposite direction, so the stars appear stationary.
I also used a drill press for drilling the holes for the sliding motor rails so that they are parallel to each other, as well as the hole for the drive rod to ensure it was nicely perpendicular. It can go either way CW or CCW on startup so you just need to check which way its going when you switch on, if its the wrong way then you just flick the power switch till it goes your required direction. Up until July of last year, I didn't even have a suitable camera for astrophotography, but with the Canon EOS M fire sale, suddenly it was a possibility, as the EOS M has a nice large APS-C class sensor in it. However, the basic design can only do short exposures, and the dual arm tracker invented by Dave Trott required a lot of relatively fine fabrication that I wasn't too sure if I could pull off. I looked through my collection of electronic bits 'n bobs, and found a stepper and its worm drive in an old HP printer carcass; a serious shortcut.
An ATTiny85 is the brains of the operation, running off a precalculated table for step rate vs. A finderscope is mounted near the hinge, and a ball mount is plopped in the middle of it (the location of the ball mount does not particularly matter - took me forever to figure that out!). This gives the rate of change at time t, with V being the desired tracking rate, S the starting angle, and A and B the two sides of the triangle. First, you point the tracker roughly north, and set the altitude to what is correct for your latitude - Polaris's altitude is roughly equivalent to your latitude.
It could run for something like 5 days straight, too bad it'd run out of rod after 70 minutes! On start, a variable specially marked not to be initialized is read; if it's not a special value, a rewind is executed, and at the end of the rewind, the special value is stored in the variable.
Paul Stoffregen's code will work; it can deal with clocks of 1mhz, 2mhz, 4 mhz, 8mhz, and 16mhz.
These programs should compile fine under any *nix based OS, windows would need to edit the makefiles.
A small bolt was run through the top board and a wire connected to it, altogether forming the limit switch used for rewinding. Recommend milk jugs, plastic bags are a lot harder to melt down into a nice chunk of plastic stock. Fused together a nice slab of plastic from milk jugs, bent it slightly, and drilled the relevant holes in it. Over a few design iterations, I had found that a slippery plastic washer gave a nice smooth adjustment against the original metal mounting, rather than nasty, gritty metal on metal contact.
Note, the stuff lowes' sells is really brittle but strong; if you are going to bend it, don't bend it sharply and suddenly, it will just snap. It's not ideal, but it's fairly sturdy, especially with the addition of a 8lb brick (and 4lb battery) hanging off some paracord underneath it. The eye relief on those things is murderous - the required distance from scope to eye, and the image is rather dim due to the small aperture. The dead space was murderous when trying to keep track of how many turns I tweaked, so ended up reinforcing it a lot to get down to nearly no slop. I fried my poor teensy microcontroller and a stepper driver by accidentally connecting motor power (+12v) to the logic power bus (+5v).
I tried to improvise one out of some PVC couplings and a wood ball, like others have done, didn't work very well. If the stars are sharp in that, you've got a mount problem, either alignment, tracking, or vibration; not a focus problem. This should be done parallel to the hinge, around 4cm along, as shown in the diagram below (click for larger view).. The main pivot is constructed from an M8 size barrel nut available here which slots into a 12mm hole drilled into the side of the upper board of the mount, making it more robust and accurate. Drilling a second hole (12mm diameter) in the side of the upper board to intersect the larger hole (as pictured) allows the barrel nut to be slid into place, and the drive mechanism to be positioned.
The smaller size hinge also gives less play and greater accuracy of movement compared to something like a door hinge. This is probably the one change which had the biggest impact on accuracy and consistency of shots. With this you can cut out a series of markers, then using a protractor place them around the path of handle at 30 degree intervals (5 seconds on a clock face). The laser or scope can then be adjusted in the bracket until they both point exactly at the same target star. If you don’t have live view, autofocusing on a distant object before the sun sets works well. This exposure of the Orion Nebula with a 180mm f2.8 lens shows how well the barn door tracker works, even with subjects near the celestial equator. All of the photos in this gallery were taken by me in a light polluted back garden, with a standard SLR camera and the ?10 barn door tracker. Ordered a camera ball mount and A4988 stepper driver, made a pivot for the salvaged stepper, made a pivot nut, then bought some wood, blah, blah, work, math, etc and then I had this tracker dingus. Another piece of threaded rod controls the altitude of the tracker and the final bit of rod is used to rotate the base of the mount (azimuth) - my workaround for not wanting to buy a proper tripod. Keep in mind the altitude adjustment needs to cover the range where polaris normally is, though. Even if you are planning to go with a powered mount, I'd still consider something like the curved rod tracker described here.
For short exposures you can even get away without changing the RPM at which the shaft is turned, for a short time. Not sure if it's giving me trouble or not but I'd just have soon not had to worry about that in the first place. The derivative of the law of cosines is used to calculate the initial rate, but after that it's just a bit of brute force.
This is used to by the calculator to find angle S, the initial angle between the two pivots. Note, this is not a general derivative, as it uses the function for determining target angle at time t; W(t) = S + t * V. Repeats until $MAX_TIME is reached, and then prints out the resulting table of values noting where corrections to the rate should be made. Then, look for either cassopeia or the big dipper, depending on time of year, to determine the angle the NCP is relative to polaris.

You could just easily use a bigger uC (more pins) such as an ATtiny84 or ATMega part, I just didn't have space left on the beater breadboard that I didn't mind semi-permanently installing. The AVR's pin 1 (RESET) is connected to the pushbuttons for user input (which connect to ground).
I also got a third IR LED, put salvaged connector on it, and glued that to the camera part of the ball mount. The canon solution is a dummy battery with a power jack in the bottom; the EOS M has a rubber flap on the bottom of the battery door to allow access to the jack. If the user resets the uC via the buttons connected to RESET, the memory will still contain the special value, so when the program starts again the code will read the var, see the special value, and then run normally after clearing the variable. After this point, if the user is using the momentary push button, they presumably let go and power is lost. Drill a large hole (or cut a slot) in one end of the 14 inch boards for the drive rod, put half of the piano hinge at the other side.
A more elegant solution would be to purchase a proper dovetail receiver, but this works just as well and I had the parts handy. However, there was some flex in the bodged up metal support, and the plastic washer was fiddly - it was possible to knock the mount out of alignment by lifting the board up slightly and having the washer settle in a different manner.
Receiver of the rod (near the hinge) was made out of another chunk of milk jug derived plastic, bent with a hot air gun. Two vex parts are used for the pivot, but you could use carefully bent mecanno strips too, or make some out of milk jug plastic. I removed the assembly from printer, cut off all the extra bits of plastic, opened one side of the gear bit, screwed the threaded rod into the gear, and mounted it on a pivot made out of some plastic bits from a VEX set. The telescope mounted by two threaded inserts in its base; I drilled two large holes at the appropriate spots in the bottom bit of wood, forced a nut in there with superglue, and superglued a large washer over each. I tried to improvise one out of some PVC couplings and a wood ball, but even if it had worked the result would have been extremely crude to use, especially without knocking the mount out of alignment, and severely limited as to max altitude. So basically, I couldn't tell when my eye was in the right place or not because all I saw was black.
Even if it had worked the result would have been extremely crude to use without knocking the mount out of alignment, and severely limited altitude-wise (can't aim high enough), Just pay the 17$ for a solid mount, it's worth it.
Again, I’ve seen lots of trackers online, but none of them seem to have this simple addition. Then, I saw the Cloudbait observatory tracker build, which introduces a more elegant solution: controlling error by varying drive speed, rather than mechanically compensating like the dual arm design. The microcontroller is what makes this mount special, and lets it actually track for any extended period of time. Note where graph shows the RPM oscillating between two values - this is where an integral value would be too slow or too fast to match the ideal tracking rate. Depending on the focal length of the lens you intend to use, this may be all that is required. Here's a diagram to help with that, and here's the reversed version; how it looks through a finder scope.
There will be alignment error between the scope and mount, the angle won't be perfect, and the distance won't be exact, but to what degree this effects you depends on the lens you are using. Whatever you use for the controller, if you want to use longer focal lengths, you will need a crystal, as the RC oscillator built into an AVR is temperature sensitive and inconsistent.
A 100uf electrolytic capacitor and 0.1uf ceramic capacitor are connected between +12v and ground. This allows me to control the EOS M via a wired connection rather than having to reach around with the remote or place the remote where it can be seen by the camera's IR receiver.
I made a dummy battery out of a solid chunk of milkjug-derived plastic, added contacts and a jack, salvaged a LM317 adjustable regulator (set it to 7.7v), and stuck that in an AC adapter's casing; done! This allows me to not have to burn the "reset as IO" fuse bit, which would prevent me from programming the AVR without removing it. I sighted in the scope by making a reflex sight out of a straw and some thread, then taped to the hinge and sighted it in during the day. Heated it up with the hot air gun after fusing bags together, then bent it at a 90 degree angle with the aid of a piece of wood.
So, I tried to find a chunk of a similar plastic (HDPE) that I could make a new, stronger mount out of. The resulting material is very easy to drill, easy to cut with a hacksaw, easy to dremel, pretty much a dream to work with.
Also, it lets you see where exactly the NCP is relative to polaris - remember to invert the position if using a finder scope. The orange lines on the right side highlight the group of stars which act as a sort of arrow. I've been having some issues earlier in the run at that focal length, but I think I've gotten those fixed, pending testing (clouds). You'll also have to directly measure the length of the drive rod between the two pivots, which is the starting length C. I printed the reversed diagram, "laminated" it with some tape and cardboard, then stuck a pin in the center on the top of the tracker, so I can rotate it relative to the position of the constellations.
You may need to take exposures and make tweaks to the axes until no trailing is evident, if you are using an long telephoto lens or have a telescope mounted. Once I have the tracker set up and camera aimed, I can walk away while the camera happily takes exposures without me. Plus, once I get it aligned and set on a target, I can leave it alone while it takes pictures for me! In reality, it depends on your measurements and how well you've aligned the mount, as well as how accurate the drive rod is.
Turns out to have been a godsend as my initial delay table wasn't even in the right ballpark. For the pivot, I went through about 5 different designs trying to reduce slop in the axis, but this final overbuilt design has reduced slop to nearly nothing. Very strong, but still with a bit of flex, and has the characteristic slipperiness of HDPE. You could also use Stellarium to figure it out, too - I find turning on both equatorial and azimuthal grids make it pretty easy to judge the angle, in practice, I use that more often than the disk.
I think anything but the shortest focal length telescopes are probably beyond this type of mount, though - would be too hard to align and required precision of tracking too high.
An ISP header is present and connected to the relevant pins as well as hooked to the +5v bus via a diode to allow programming without the battery attached. It's only about 60% efficient, as the LM317 burns waste energy as heat, but it's still enough for over 6 hours of use with a 7AH battery with the tracker active.
When rewinding, it goes until it hits limit switch, advances a little, then fully shuts down the AVR after putting the A4988 in a sleep state. Drill a nice big hole through each of the 7 inch boards, put a bolt through them with washers on top, bottom, and in-between boards. Plastic bags are made out of the same plastic, but it's a lot harder to reduce them into nice coherent chunks of plastic. Overall, a serious score; possibly wouldn't have even made this mount if not for finding it.
Plus, if I had to spend the cash, I'd rather spend it on a better telescope or camera lenses, not an extremely specialized camera mount. Put a piano hinge at one side of the upper 7in board, and screw one side to the bottom of the tracker. You could get away without making a screw driven azimuth adjustment, but you'll definitely need something to control the altitude (elevation).
I figure a 10 min shot would open the boards only 2.5 degrees but your photos show them much wider than that.
That said, it might be theoretically possible to use a Canon PowerShot (point n shoot range) and load it with the CHDK software to utilise the intervalometer scripts.

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Comments to “Barn door tracker for sale kenya”

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